This study was conducted to identify preoperative predictors of postoperative atrial fibrillation (POAF) after isolated coronary artery bypass grafting (CABG) by using a Bayesian analysis that included information from prior studies. We performed a prospective observational study from October 2008 to December 2013 of 1,481 patients who underwent isolated CABG with cardiopulmonary bypass and had no history of AF. Bayesian analysis was used to study the preoperative risks factors for POAF. The POAF incidence was 21%. Multivariate analysis identified the following independent predictors of POAF after CABG: high CHA DS -VASc (Congestive heart failure, Hypertension blood pressure >140/90 mm Hg or treated hypertension on medication, Age ≥75 years, Diabetes mellitus, prior Stroke or transient ischemic attack or thromboembolism, vascular disease, Age 65 to 74 years, Sex category female sex) score (odds ratio OR, 1.23; 95% credible interval CI, 1.14 to 1.33 per 1-point increment, probability (Pr) OR > 1 = 1), severe obesity with a body mass index of 35 kg/m or higher (OR, 1.28; 95% CI, 1.12 to 1.45; Pr OR > 1 = 1), preoperative β-blocker use (OR, 1.12; 95% CI, 1.06 to 1.20; Pr OR > 1 = 1), preoperative antiplatelet therapy (OR, 1.75; 95% CI, 1.14 to 2.79, Pr OR > 1 = 1), and renal insufficiency with a creatinine clearance of less than 60 mL/min (OR, 1.34; 95% CI, 1.03 to 1.74; Pr OR > 1 = 1). This prospective Bayesian analysis identified five independent preoperative predictors of POAF after isolated CABG with cardiopulmonary bypass: CHA DS -VASc score, severe obesity, preoperative β-blocker use, preoperative antiplatelet therapy, and renal failure. The main interest in the CHA DS -VASc score as a predictor of POAF is that it is a simple and widely used bedside tool. Patients with these independent predictors of POAF may constitute a target population to test preventive strategies, such as non-antiarrhythmic and antiarrhythmic drugs.